<template>
  <ul class="list">
    <li class="item" v-for="(item,key) of letters" :key="item"
        :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
    >{{item}}
    </li>
    <!--<li class="item">A</li>-->
  </ul>
</template>

<script>
  export default {
    name: 'CityAlphabet',
    props: {
      cities: Object
    },
    data() {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
    },
    computed: {
      letters() {
        const letters = []
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters
      }
    },
    updated() {
      this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
      handleLetterClick(e) {
        this.$emit('change', e.target.innerText)
      },
      handleTouchStart() {
        this.touchStatus = true
      },
      handleTouchMove(e) {
        if (this.touchStatus) {
          if (this.timer) {
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 75
            const index = Math.floor((touchY - this.startY) / 20)
            if (index >= 0 && index < this.letters.length) {
              this.$emit('change', this.letters[index])
            }
          }, 16)
          // const startY=this.$refs['A'][0].offsetTop

        }
      },
      handleTouchEnd() {
        this.touchStatus = false

      }
    }
  }
</script>

<style scoped="scoped">
  .list {
    display: flex;
    flex-direction: column;
    justify-content: center;
    position: absolute;
    top: 1.74rem;
    right: 0;
    bottom: 0;
    width: .4rem;
  }

  .item {
    line-height: .54rem;
    text-align: center;
    color: #25A4BB;
  }

</style>
